He was a normal 18 month old with a 10 word vocabulary. Then two days after Jeremy received a shot for diphtheria, whooping cough, and tetanus, he was in the hospital.

Click play to watch CBN coverage of the pros and cons of vaccinations. Does evidence suggest they cause diseases in children? Gailon Totheroh explains.

"He was hospitalized two days after the shot and he was running a fever of 103. And he was so hot that the nurse that was standing there could feel the heat radiating off his body." Jeremy's mother Lynn said.

For the last 29 years, Jeremy has not spoken an intelligible word.

Cases like this are not uncommon -- 4,500 families are suing the government because they believe vaccines caused their child's autism.

Since the 1980s, critics have questioned the safety and effectiveness of vaccines. Government health officials and most doctors insist the benefits are large and the problems exaggerated.

"The risks are far greater to your child of not getting immunized than any kind of speculative potential relationship between the vaccine and the development of autism," said Irwin Redlener, MD, Columbia University.

Barbara Loe Fisher of the National Vaccine Information Center says there are real problems, but many doctors are in denial. She said, "It can't be true -- because how, how, could they possibly really live with the idea that something that they try to do that was good - has turned out to be bad for a lot of people."

Now a June survey of more than 10,000 families suggests the problems are more than speculative.

It found teenage boys vaccinated as children were:

Twice as likely to suffer from autism

Four times as likely to have Attention Deficit/Hyperactivity Disorder

And boys and girls of all ages - vaccinated as children - were more than twice as likely to have developed asthma.

At one time, Beth Miers thought vaccine critics were kooks.

"That's crazy, why would you not vaccinate your child?" Meirs believed. "You want to put your child in danger of developing those diseases? And so I really did think these people were way out there."

But her mind changed in March when a doctor found that her daughter, 8-year-old Emma, had high levels of toxic mercury - a preservative used in childhood vaccines until recently.

Beth first became suspicious last October after Emma had a flu shot.

"It was almost a depression, and she was having… negative thoughts that bothered her and she would say, 'Mommy I'm having the bad thoughts, I want them to go away.' And we would pray for them to go away-- and it was very concerning," Beth said.

She then began to look back and connect that with changes in Emma's behavior after she received shots as a toddler.

Emma ".developed allergies at 2 which is pretty young. sensitive to clothing, to heat. she would fall very easily. she reacted so strongly, just tears and screaming. those kinds of things, it just didn't seem right," Beth explained.

Emma showed some improvement after going on a healthier diet several years ago, but still struggled. Now with medical treatment to remove the mercury, taking supplements, and a diet free of wheat and milk, she's doing better.

"I would have really bad nightmares," Emma said. "And I also used to see colorful spots, and they also went away, too."

No one knows how many Emmas are out there -- subtle cases that never make it into the medical statistics. Many neurological experts consider such cases part of a spectrum of vaccine afflictions, from the tiniest damage to ADHD up through the worst, autism.

Mercury was taken out of kids' vaccines by 2004 - though not the flu shot - but vaccines still contain aluminum and dozens of other potentially harmful ingredients.

One of them is monosodium glutamate, or MSG - a potentially toxic flavor enhancer in some foods - yet an ingredient in many vaccines. John Erb has investigated vaccines as part of his work with autistic kids in the last 20 years.

Erb said, "If there are glutamate-bearing ingredients in that vaccine, think twice. Because science has proven for the last three decades that glutamate has a huge effect on living beings."

Brain expert Dr. Russell Blaylock believes much of the problem from vaccines is their effect on the cells of the brain's immune system called microglia.

For example:

Invaders like viruses and bacteria activate the microglia, which return to normal after the threat.

But vaccines - especially multiple vaccines injected the same day - can put the microglia into constant battle mode.

In that mode, the brain turns on itself, causing what's known as "bystander damage."

A leading neurology journal seemed to confirm this with autopsies of autistic brains.

".They found all of them had over-activation of the brain's microglia, chronic brain inflammation, which is by this mechanism," Blaylock said.

Mercury, aluminum, and MSG are powerful activators of the microglia -- linking brain damage with vaccines. Fisher says the vaccine companies try to exclude that damage.

She explained, "The manufacturers conduct clinical trials and whenever anything bad happens in that clinical trial -- nine times out of 10 if not 10 times out of 10 -- they write off the health problem that occurs or the death that occurs as a coincidence."

So what can parents do to at least limit the side effects?

Don't vaccinate a child who is sick or has had a previous severe vaccine reaction.

Be careful about giving multiple vaccines on the same day, especially to premature babies.

Tell your doctor if your child or your family has a history of autoimmune or nervous system disorders.

Learn vaccine side effects so you can monitor your child after vaccination. In case of problems, immediately call your doctor.

Blaylock says, also, that the most important thing is good nutrition to build a strong immune system.

That's not just theory, that's history. The fall of mass death from infections occurred when nutrition improved on a large scale.

"When they looked at diphtheria and they looked at measles and they looked at all these infectious diseases that were killing so many people, they found a 75 percent, 90 percent, 50 percent drop in the number of people who were dying before the vaccine programs were ever started," Blaylock said.

In other words, the drop had nothing to do with the vaccines.

That kind of information is needed by parents, Fisher believes. Know the risks and the benefits. Then make an informed decision. And know that vaccine policy may need radical reform, so parents are allowed to pick and choose what's best for an individual child.

"We have to individualize the policies to begin with," Fisher said. "But we have to do the scientific studies to really determine whether a policy of using 48 doses of 14 vaccines before age 6 is a wise policy."